Sprag Woes

Well, I've shagged my sprag!
After problems with a new solenoid and having to rely on the electric leg only while commissioning the bike I went to take it for only its third 15 minute break-in run and ......press........clank........whirrrrr!

Stripped the primary and sure enough, notches in the engine sprocket and on outside of the gear, and buggered sprag.
I will order new ones from ANIL tomorrow. I notice the gear with the needle brg has gone up 20pd's since I last looked!!

Brings to mind two related points.

1. What are all Mk3 owners running in their primaries? I remember, I think it was Millard was told by Norman White to run fork oil "with a dash of engine oil".
There are a lot of opposing requirements here. Cooling of the alternator, enough viscosity to work in the chain tensioner, lube of the chain itself and the starter gear, just enough of whatever to do all this succesfully but not contaminate the clutch and promote drag or slip!!
Tall order!

2. While stripping the alt/starter parts it once again occured to me that it is a big ask to expect the chain to pick up oil and throw enough around to work its way all the way in there to the sprag! Especially when centrifugal force is trying to fling it away!
I assembled it last time with plenty of engine oil but this time I think I will be liberal with some HTB grease. What does the brains trust think?

Hi Shedweller
Sorry to hear about your sprag problems.
I’m glad to hear that you’re going to bite the bullet and replace all the related components at the same time as well, that’s a very wise move.
When I purchased my commando several years ago the owner was using Dextron 2 automatic transmission fluid in the primary and I’ve continued to use it too.
I’ve had no problems with its viscosity affecting the operation of the primary chain tensioner or any problems with the clutch dragging or slipping.
In fact a car’s automatic transmission is a far more hostile environment than a Norton primary can ever be; it runs at far higher temperatures and at far greater loadings.
Surely by its very design fork oil will have lots of anti- foaming and anti- sludging additives and as its not really designed to get much more than slightly warm is it really a suitable oil to use in the primary without it quickly breaking down?
I’m sure wiser people on the board will be able to answer that point, but that’s my thoughts anyway.
I hope you soon get it all back together and back on the road again.

shedweller said:

1. What are all Mk3 owners running in their primaries? I remember, I think it was Millard was told by Norman White to run fork oil "with a dash of engine oil".

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To quote Millard "when I was at Norman White's a coupla weeks ago getting my gearbox looked at, he told me to use fork oil topped up with a wee bit of engine oil."

When I bought my own Mk3 it had ATF in the primary, which I continued to refill it with myself, until I read that ATF possibly wasn't the best thing to use with the Mk3 hydraulic tensioner, so I tried 10w/40 (the original spec. is 20w/50) engine oil, and not only did the primary drive appear to run more quietly, but there was a noticeable reduction in transmission snatch when riding slowly using low revs, and there have been no clutch problems since. So personally I would not recommend using ATF (or fork oil?) in a Mk3 primary case fitted with the original tensioner.

shedweller said:

I assembled it last time with plenty of engine oil but this time I think I will be liberal with some HTB grease. What does the brains trust think?

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I don't believe the sprag unit needs much lubrication, and I'm not sure using grease would be a good idea, as the oil will probably wash it out anyway? And grease could make the sprag slip?

You have not said if your blown sprag unit is the original 14 sprag type? The latest type has 18 sprags and the rings are possibly a little more robust? Fitting all three new parts together is recommended (engine sprocket/sprag/gear) as I think you will be doing, and Norvil for instance, won't give a full warranty on them unless all three parts are fitted together. http://www.norvilmotorcycle.co.uk/064733.htm

One thing I would suggest that you (and any other Mk3 owners?) should check is the slip torque of the starter drive anti-backfire device, as it should prevent the sprag and the rest of the starter drive from being overloaded if the engine decides to kick back. The starter A/B device should slip at 50 ft/lbs of torque.

I think many owners have over-adjusted the A/B device after they've heard it slipping, but of course it *should* slip if the starter drive becomes overloaded.
When my (14 piece) sprag broke, I found the A/B device had been over-adjusted so far by a previous owner that it was locked solid!

Happy New Year Shedweller!

My only concern about using ATF in the primary is the possibility of it mixing with the engine oil. There is a remote chance of this occurring should your crankshaft seal unknowingly fail. I assume that the ATF would dilute the protective properties of the engine oil? Or, perhaps my concern is unfounded.

I use 20W 50 in the primary of my MK 3, but I no longer have the starter, sprag clutch, etc. installed - it's a kick-only Mark 3. I used the end cap from the starter to cover the huge hole in the inner primary that remained after removing the starter motor. Following is a picture of this arrangement.

I'm running a belt on my MK3 primary, with all starter gear in situ and working.

There are a lot of people (who may prove correct, I'll let you know) who believe that the lack of lubrication will kill the sprag. Mine has done about 1200 miles up to now with no problems.

Mr. Emery has instructed me to lubricate it occasionally, and I have done it once with constant velocity type grease, and will probably do it before the start of next season. As I use the belt, I get no clutch slip.

L.A.B. wrote.

One thing I would suggest that you (and any other Mk3 owners?) should check is the slip torque of the starter drive anti-backfire device, as it should prevent the sprag and the rest of the starter drive from being overloaded if the engine decides to kick back.

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When I built and checked my anti backfire device, I did it this way. I assembled the left hand parts of the shaft (when sitting on the bike), not locking the starter shaft shouldered nut, mounted it in some soft jaw vice by the "gear" and slid on the right hand side of the shaft the thrust washer 065652, which I had groud into a suitable hexagonal shape for a socket to fit. I attached my torque wrench to the socket, and used the torque wrench on this modified thrust washer to turn the shaft, to get the preload set, which is done by tightening/releasing the lockring nut. When it is set to the correct torque, tap the lockring down to lock itin position, and take this modified thrust washer off, build up the right hand side and fit.

I hope this makes sense. I can't find my worshop manual at the moment, and can't remember what the "proper way to do it is," but found it quite easy by modifying a spare thrust washer that I had. :idea:

Reggie said:

I can't find my worshop manual at the moment, and can't remember what the "proper way to do it is," but found it quite easy by modifying a spare thrust washer that I had.

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Actually I don't think the factory manual says anything about adjusting it at all, although the Haynes manual does. No "proper way" of adjusting it is mentioned, but the ground-down thrust washer seems to be a good idea.
I did it by inserting some short lengths if welding rod between the shaft splines and then used a tight fitting socket over them.

I'd certainly agree that if the primary is run "dry" because of a belt kit etc. then some periodic lubrication of the sprag would be needed.

Thanks for the tips, guys. LAB, the bike had no start gear when I bought it as a basket so I bought a set (minus starter) from a contact in NZ. Turned out the (14 element) sprag was U/S so I bought the three elements from nick at ANIL. That is why it hurts so much!
Having bought them, made up huge cables, new solenoid (which then failed and is likely to have contributed to this failure) a Comeau starter and PC545 battery it is a bit late to back out. I only used the other elements from NZ but did not strip the AB unit as I assumed it would be OK. I will now attend to it (thanks Reggie) in detail and ensure it is at correct slip setting.
I am still a bit undecided about the lube oil. There are valid arguments for the different types due to the conflicting requirements. I guess I have time to sleep on that. The bike is going nowhere for a while.......

ATF for me for the last 7 years in my MKIII with no problems what so ever. I had been using 20/50 but found too much clutch drag. I have a functional starter and no lubrication issues with the sprag.

I'm on the fence right now about going with a belt drive or sticking with the stock arrangement on my MKIII.

For the belt drive guys, are you adding extra vent holes on your primary?

Coco wrote

For the belt drive guys, are you adding extra vent holes on your primary?

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No. I'm not. The primary still looks standard on mine.

I would fit some meshed inspection caps if I could source some though.